The Federal Communications Commission (FCC) requires that power converters operate with limited radiated emissions to prevent electromagnetic interference (EMI) with other devices. Power converters are particularly susceptible to EMI issues due to the high power levels that are often present. Furthermore, power converters are increasingly operating at higher frequencies to reduce the value and corresponding size of components such as inductors and capacitors. High operating frequencies produce high order harmonics, which further contributes to EMI.
Methods to reduce EMI in power converters have included using snubbing circuits to absorb high frequency transients, commonly found with stray inductance experiencing a step function or discontinuous conduction. Snubber circuits may be formed by an attenuating circuit with resistors and capacitors connected by a diode to a node experiencing the transient behavior. Snubber circuits are inefficient because they waste the energy from the transient signal that is being snubbed. Another method for reducing EMI relies upon spectral spreading to spread the noisy signals over a sufficiently wide bandwidth such that each signal radiates less than the allowable EMI limit. Spectral spreading is problematic in resonant and quasi-resonant power converters because it relies upon changing the timing of a signal that must be aligned with a trough of a resonant signal to minimize switching losses.